Tunnel magnetoresistance element having a double underlayer of amorphous MgO and crystalline MgO(001)

Abstract

By varying only the thickness of a known material having superior magnetic characteristics to increase spin polarization without changing the chemical composition, a tunnel magnetoresistive element capable of producing a larger magnetoresistive effect is provided. The tunnel magnetoresistive element includes an underlayer (nonmagnetic or antiferromagnetic metal film); an ultrathin ferromagnetic layer disposed on the underlayer; an insulating layer disposed on the ultrathin ferromagnetic layer; and a ferromagnetic electrode disposed on the insulating layer.

1. A tunnel magnetoresistive element having a substrate, a double underlayer including an amorphous MgO layer and a (001)-oriented MgO layer, and a tunnel magnetoresistive effect portion, in this order. 
     
     
       2. A tunnel magnetoresistive element according to  claim 1 , wherein the thickness of the amorphous MgO layer is set in the range of 3 to 10 nm and the thickness of the (001)-oriented MgO layer is set in the range of 3to 10 nm, and thereby surface roughness is reduced. 
     
     
       3. A tunnel magnetoresistive element according to  claim 1 , wherein, by using the underlayer, roughness of a ferromagnetic layer is reduced and magnetostatic coupling between ferromagnetic layers is reduced. 
     
     
       4. A tunnel magnetoresistive element according to  claim 1 , wherein, by using the underlayer, roughness of an ultrathin ferromagnetic electrode layer with a thickness of 15 atomic layers or less is reduced and the magnetoresistive effect is increased. 
     
     
       5. A tunnel magnetoresistive element according to  claim 1 , wherein a nonmagnetic layer with a thickness of 20 atomic layers or less is disposed between a barrier layer and a ferromagnetic electrode layer, and those layers are disposed between the underlayer and the tunnel magnetoresistive effect portion thus the bias dependence of magnetoresistive effect is controlled. 
     
     
       6. A tunnel magnetoresistive element according to  claim 1 , wherein, by using the underlayer so that a ferromagnetic electrode layer is oriented in the (001) direction of a body-centered cubic lattice, a face-centered cubic lattice, or a tetragonal lattice and using a (001)-oriented MgO layer as a barrier layer, a magnetoresistive effect is produced.